Fabrication, Elisabeth Smela, Professor, Mechanical Engineering, University of Maryland

Fabrication

Bilayers | Self-Folding Boxes | Moving Si Plates | Origami Flower | Thickness Color Chart

Polymer Deposition

Conjugated polymers can be deposited in a variety of ways, but are typically deposited electrochemically or by spin coating or casting. For a chart showing the color of PPy(DBS) as a function of film thickness, see below.

For further information, see:

"Microfabrication of PPy microactuators and other conjugated polymer devices," E. Smela, J. Micromech. Microeng, 9, 1-18, 1999.

Bilayers

These were made using surface micromachining. First, a layer of Cr was evaporated onto a Si wafer and patterned to leave rectangular openings. A film of gold was evaporated onto it. Next PPy was deposited and patterned. Finally, the exposed Au was etched away.

Instead of using a sacrificial layer, the release was accomplished using differential adhesion: the Au layer sticks to Cr but not to Si. When the PPy is electrochemically cycled, the bilayer bends, coming off the surface.

For further information, see:

"Controlled Folding of Micron-Size Structures," E. Smela, O. Inganäs, and I. Lundström, Science, 268(5218), 1735-1738, 1995.

Self-Assembling Boxes

These were also made using surface micromachining and differential adhesion was used for release.

For further information, see:

"Controlled Folding of Micron-Size Structures," E. Smela, O. Inganäs, and I. Lundström, Science, 268(5218), 1735-1738, 1995.

Moving Si Plates

Bulk micromachining was used for these devices. Al was sputtered onto both sides of the wafer and patterned using a double-sided aligner. Reactive ion etching (RIE) defined the plate, and the etching was halted with a thin layer of silicon remaining. The Al was removed and an oxide deposited by chemical vapor deposition (CVD).

For details, refer to:

"Electrochemically Driven Polypyrrole Bilayers for Moving and Positioning Bulk Micromachined Silicon Plates," E. Smela, M. Kallenbach, and J. Holdenried, J. Microelectromechanical Systems, 8(4), 373-383, 1999.

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Origami "Flower"

These structures were made using bulk micromachining, like the moving Si plates. The close-up schematic below shows how each petal was contructed from numerous parallel polyimide plates connected by long, thin bilayers.

Thickness Color Chart

The color of PPy(DBS) deposited on Au changes as it increases in thickness up to ~1 mm (after that it appears black), as shown in the color chart below. The color is therefore a good indication of the thickness. Bear in mind that the colors shown here are for dry films, and will be different from what you see when the films are immersed, or recently removed from water.